Results In NETHCON, a lower percentage of LBC samples were judged to be unsatisfactory compared with CC samples (0.33 versus 1.11%). There was no significant trend in unsatisfactory results by age group for conventional cytology (Ptrend = 0.54), but there was a trend towards an increasing percentage of unsatisfactory results with increasing age for LBC (Ptrend < 0.001). In NTCC, a lower percentage of LBC samples were judged to be unsatisfactory compared with conventional cytology (2.59 versus 4.10%). There was a decrease in the unsatisfactory results by age group with conventional cytology (Ptrend < 0.001) and with LBC (Ptrend = 0.01), although the latter trend arose from the 55–60-years age group (Ptrend = 0.62 when excluding this group).

Conclusions The clinical trial in which the results were collected and the cytologic method used were the most important determinants of unsatisfactory cytology. In all situations, the proportion of unsatisfactory samples was lower in LBC compared with CC. The effects of age depended on the criteria used to define unsatisfactory results.